Nitric Oxide
Nitric oxide (NO) is a molecule of importance in several biological systems, and is continuously produced in the lung and can be measured in ppb (parts per billion) in expired gas. The discovery of endogenous NO in exhaled air, and its use as a diagnostic marker of inflammation dates back to the early 1990-ies (See the published international patent applications WO 93/05709 and WO 95/02181). Today, the significance of endogenous NO is widely recognized, and since a few years back, a clinical analyzer is available on the market (NIOX®(, the first tailor-made NO analyzer for routine clinical use with asthma patients, AEROCRINE AB, Solna, Sweden).
The American Thoracic Society (ATS) has published guidelines for clinical NO measurements (American Thoracic Society, Medical Section of the American Lung Association Recommendations for standardized procedures for the online and offline measurement of exhaled lower respiratory nitric oxide and nasal nitric oxide in adults and children—1999, in Am J Respir Crit Care Med, 1999; 160:2104-2117).
It is generally recognised that endogenous generation of the gaseous NO molecule plays an important role in the modulation of pulmonary vascular tone to optimise ventilation-perfusion matching (Persson et al. 1990). In healthy human adults, NO is of importance in regulation of both basal pulmonary and systemic vascular resistance (Stamler et al. 1994). Local regulation of blood flow is influenced by administration of NO synthase inhibitor in healthy human subjects (Rimeika et al 2004). Vasodilator effects of endogenous NO in the postnatal pulmonary circulation clearly contribute to the adaptations of the fetal lung to air breathing at delivery (Abman et al. 1990). NO generation in the postnatal lung is stimulated for example by mechanical stretch, increased shear forces and increased O2 tension in the alveoli (Heymann 1999). Measuring NO in exhaled breath is a good way of monitoring changes in endogenous NO production or scavenging in the lung (Gustafsson et al. 1991).
Further, U.S. Pat. No. 5,670,177 discloses a method for treating or preventing ischemia comprising administering to a patient by an intravascular route a gaseous mixture comprising NO and carbon dioxide CO2 wherein the NO is present in an amount effective to treat or prevent ischemia.
U.S. Pat. No. 6,103,769 discloses a similar method, with the difference that saline, saturated with NO, is used.
The published international application WO 94/16740 teaches the use of NO delivering compounds, such as S-nitrosothiols, thionitrites, thionitrates, sydnonimines, furoxans, organic nitrates, nitroprusside, nitroglycerin, iron-nitrosyl compounds, etc, for the treatment or prevention of alcoholic liver injury.
Nitrates are presently used to treat the symptoms of angina (chest pain). Nitrates work by relaxing blood vessels and increasing the supply of blood and oxygen to the heart while reducing its workload. Examples of presently available nitrate drugs include:
Nitroglycerin (glyceryl nitrate) (1,2,3-propantriol-nitrate), which is today mostly taken sublingually to curb an acute attack of angina. Strong headaches and dizzyness due to the rapid and general vasodilatory effect are frequently encountered side-effects. Nitroglycerin infusion concentrates are also available, and diluted in isotonic glucose or physiological saline for intravenous infusion. Tolerance development is a problem both in acute and in long-term treatment regimens.
Isosorbide mononitrate (1,4:3,6-dianhydro-D-glucitol-5-nitrate), which is taken as prophylactic against angina pectoris. Tolerance development is a problem in long-term treatment regimens. Frequent side-effects include headache and dizziness, as encountered with nitroglycerin.
Isosorbide dinitrate (1,4:3,6-dianhydro-D-glucitol-2,5-nitrate), which is taken both acutely and prophylactically against angina pectoris and cardiac insufficiency.
Pentaerythrityl nitrates, a group of organic nitrate, are known to exert long-term antioxidant and anti-atherogenic effects by as yet unidentified mechanisms. Pentaerythrityl tetranitrate has been investigated in the context of nitrate tolerance, an unwanted development in nitrate therapy, and experimentally tested in pulmonary hypertension.
A number of compounds, glyceryl trinitrate, ethyl nitrite, isobutyl nitrate, isobutyl nitrite, isoamyl nitrite and butyl nitrite, have been tested in vivo and found to generate NO (Cederqvist et al., 1994). Significant correlation was obtained between in vivo generation of NO and effects on blood pressure in a rabbit model.
Accordingly, it has been suggested in U.S. Pat. No. 5,646,181 that certain organic nitrites traditionally synthesized, have utility in treating male impotence and erectile dysfunction through topical or intracavernosal administration to the penis.
Inorganic nitrates and nitrites, such as potassium nitrite and sodium nitrite, have a long use as food preservatives. Nitrates and nitrites have in general been considered to be potentially harmful, due to the theoretically possible formation of carcinogenic N-nitroso compounds in food, and in humans in vivo. Lately, the role of dietary nitrates and nitrites has been re-evaluated, in particular as the endogenous production of NO in the arginine-nitric oxide system and its role in host defence has been discovered (Larsen et al., Effects of dietary nitrate on blood pressure in healthy volunteers, N Engl J Med 355, 2792-3 (2006)).
Finally, L-arginine, and esters thereof, such as the ethyl-, methyl- and butyl-L-arginine have been used to increase the endogenous production of NO.
WO 96/38136 discloses nitrosation of proteins using gaseous nitric oxide under anaerobic conditions, forming nitric oxide adducts used to coat the surfaces of devices to be introduced into the human body. Related patents are U.S. Pat. No. 6,352,709 and international patent publication WO 96/35416.
Among the compounds and compositions presently available, many are associated with undesired properties or side-effects, such as toxicity problems, stability problems, delayed action, irreversible action or prolonged action, etc. One particular problem, frequently encountered when administering a NO-donating compound in the form of an infusion, is the production of methemoglobin (metHb).
One objective behind the present invention was to develop improved methods for the production and handling of NO-donating compounds, such as organic nitrites, and the production or formulation of pharmaceutical preparations containing such compounds. Known organic nitrites and their therapeutic use are frequently associated with problems likely to be due to impurities and degradation products present in the compositions. It is also difficult to prepare pharmaceutical formulations containing organic nitrites, as the mixing steps and vehicles used may trigger further degradation. Similarly, due to the reactive properties of NO, the storage properties of such formulations are often less than satisfactory.
Another objective was to identify new methods and compositions for the delivery of NO, without the side effects or tolerance development associated with conventional treatments and drugs.
Another objective was to identify and synthesize novel NO-donating compounds.
Other objectives, the solutions reached and the advantages associated therewith will become evident upon study of the description and examples.